The present invention relates to a method for the production of nitride based hard metallid alloys from powders containing a auxiliary metal and a refractory metal chosen from the VI group of the periodic system of the elements.
The increased use of high temperature materials in industrial construction places increasing demand on the cutting tools required for machining such materials. It has been attempted to meet these demands by the production of newer hard carbide alloys. In this connection, the tendency has been toward the employment of even harder alloys. This presents a serious problem in that as a result such alloys have correspondingly increasingly low elasticity. To overcome this problem, experiments have been conducted which, instead of using as the hard material component of the alloy the conventional carbides of the metals of groups IVa, Va and VIa of the periodic system of elements, the nitrides and carbonitrides of these elements were used. It has been found that such nitrides and/or carbonnitrides do not in fact attain the hardness of the more conventional corresponding carbides although they surpass the latter in elasticity. What is more, alloys of such materials, when used as cutting tools, have a lower tendency to weld to the chips or shavings removed from the workpiece.
It was furthermore known that only carbonitrides, having a defined nitrogen to carbon ratio, display a suitable combination of hardness and elasticity. Such carbonitrides, and nitrides, nevertheless, have the drawback of being present, in the alloy, at least superficially as oxy-carbonitrides, which are extremely stable and thus very badly wetted by the alloys forming the auxiliary metal phase. As a result brittle sintered metal carbide bodies are formed.
Such further efforts have been made to improve the wettability of nitride based carbide materials. One such process, disclosed in German publication DAS 2,005,707, attempted to improve wettability of hard metal powders by coating the grains of the powder with a layer of metal carbide which would be easily and sufficiently wetted by the binder metals used in the ultimate alloy.
A second process, disclosed in German publication OS 2,043,411, employs as a starting material nitrides and carbonitrides which are low in oxygen. Such low oxygen nitrides are best obtained from pure metal components of from the corresponding metal hydrides and purified nitrogen. In this process, the temperatures required to form the nitrides is between 1400.degree. and 1800.degree. centigrade. Low oxygen carbonitrides are produced from the reaction of the nitrides thus obtained and vacuum purified carbides, at temperatures of the same order of magnitude. Notwithstanding, the nitride and carbonitride starting materials, obtained by this latter process, always contain remnants of oxygen which must be removed. Removal of the oxygen entails subjecting the material to a refining annealing treatment in the presence of metals, of the chromium group, which metals have a deoxidizing effect. It is only when the nitride or carbonitride materials are finally combined with auxiliary metal alloys containing metals from the iron group and metals from the VI group, that a satisfactory hard metal carbide alloy is obtained. This process therefore has the further drawback in that, in order to produce a serviceable hard material component, at least two high temperature reactions are necessary. This makes the process costly and time consuming. Consequently, like the first described process, wherein the nitrides are coated, the second process has not met wide acceptance, commercial success or widespread technical use.
It is an object of the present invention to overcome said drawbacks and insufficiencies by providing an improved method for producing a hard metal nitride based powder for manufacturing hard metal alloys.
It is another object of the present invention to provide a method for producing hard metal alloys having improved strength and hardness characteristics combined with improved characteristics of elasticity and ductility.
It is another object of the present invention to provide a method for producing hard metal alloys containing a nitride based alloy and an auxiliary metal.
It is still another object of the present invention to provide a method for producing a hard metal nitride based alloy in presence of refractory metals of the VI group of the periodic system of elements.
Still another object of the present invention is to provide a method for producing hard alloys from metal carbide powders, a nitride based auxiliary metal of the IV and/or the V group of the periodic system of elements or from a mixture of these refractory metals by nitridation in presence of refractory metals of the VI group of the periodic system of elements and of a finely distributed powder of metals of the iron group.
It is also an object of the invention to provide a method for producing said hard metal powder in a simple and relatively low-cost procedure.
The foregoing objects together with other objects and advantages of the present invention will be found in the following disclosure of the present invention.